Subspecies of the pathogenic spirochete, Treponema pallidum, are the agents of syphilis, yaws, and bejel. T. carateum causes the human infection, pinta. Syphilis causes epidemics in the developed world and is endemic in the developing world;an estimated 12 million people are infected every year. Yaws, bejel, and pinta occur in isolated areas of the developing world and, like syphilis, these diseases can cause chronic disability. T. paraluiscuniculi is closely related to T. pallidum and causes venereal syphilis in rabbits, but is not infectious for humans. The clinical manifestations of infection and invasiveness of these pathogenic treponemes are significantly different among species and subspecies. Moreover, infection-induced immunity against the pathogenic treponemes is weak or non-existent across species or subspecies, but is more robust within a subspecies of pathogenic treponeme. Based on these data, we have reasoned that unique genetic sequences define the different clinical diseases. Similarly, antigens that are identical among the subspecies are unlikely to be completely protective, while those antigens that are unique to species or subspecies are most likely to be critical for complete protection. The tpr gene family is thought to be relevant to pathogenesis of treponemal infection, and we have already identified subspecies-specific sequences in several tpr genes. This renewal application proposes to 1) Identify differences in the sequences of tpr genes and their encoded proteins among strains of the three subspecies of T. pallidum and in the related rabbit pathogen T. paraluiscuniculi, using focused gene sequencing. 2) Examine the levels of transcription of the tpr genes in the three subspecies of T. pallidum and in T. paraluiscuniculi, as a function of subspecies/species, tissue location, and time after infection. 3) Identify the T and B cell epitopes of selected Tpr antigens, focusing on those proteins that differ in sequence among strains, subspecies, or species of pathogenic treponemes. 4) Determine the relative contribution of subspecies- or species-specific Tpr sequences and gene expression in vaccine-induced immunity. These studies will lead to the identification of specific molecules that are important to the pathogenesis of treponemal infections and protective immunity. Relevance in lav language: Bacteria known as Treponema cause several different, serious and persistent infections in millions of people globally each year. These studies will test whether certain genes, called tpr genes, can be used to tell one infection from another and whether the immune response to these bacteria can protect against infection.